Iris bulb rot

The causative agent of this disease is Botrytis convoluta, a specialized soil-borne fungus. This pathogen is a significant concern for horticulturists, as it specifically targets the rhizomes and bulbs of various iris species, leading to severe decay and potential collapse of the plant.

The fungus is highly destructive and is primarily known to affect ornamental irises. It survives harsh environmental conditions by forming sclerotia—hardened masses of fungal mycelium—which can persist in the soil for several years, waiting for favorable conditions to germinate and infect new hosts.

Symptoms of the infection often manifest early in the spring as stunted, yellowing foliage or a failure of shoots to emerge. When the rhizome is examined, one can observe brown, mushy decay covered in a greyish fungal mat, often accompanied by black, convoluted sclerotia that cling to the decaying tissue.

The development and spread of Botrytis convoluta are significantly accelerated by cool, wet weather and poor soil drainage. High humidity levels around the root zone create a perfect environment for the pathogen to thrive, allowing the infection to move rapidly through dense plantings if left unmanaged.

Effective management requires a combination of strict cultural practices and chemical control.

• Ensure excellent soil drainage to prevent moisture buildup.
• Remove and destroy all infected plant materials immediately.
• Treat rhizomes with appropriate fungicides before planting.
• Rotate planting sites to reduce the soil-borne inoculum pressure.